Visible light responsive titania photocatalysts codoped by nitrogen and metal (Fe, Ni, Ag, or Pt) for remediation of aqueous pollutants

Various cation and nitrogen doped and codoped TiO₂ photocatalysts, such as N-TiO₂, Pt-TiO₂, N-Fe-TiO₂, N-Ni-TiO₂, N-Ag-TiO₂ and N-Pt-TiO₂, were prepared by an acid-catalysed sol-gel process. The photocatalysts were characterised by X-ray diffraction (XRD), nitrogen adsorption-desorption isotherms, UV-visible diffuse reflectance absorption spectroscopy (UV-vis DRS), and X-ray photoelectron spectroscopy (XPS). The activities of the photocatalysts were evaluated in photodegradation of phenol solutions under simulated sunlight irradiations. A negative effect of some transition metals (iron and nickel) on photocatalysis was observed on N-metal codoped TiO₂, while enhancements in photocatalysis from noble metals (silver and platinum) were obtained. N-Pt codoped TiO₂ showed a higher activity under UV-vis irradiations than Degussa P25, with an enhancement of 5.9times higher. The synergistic effect of N-Pt-codoping was ascribed to the multivalent states of platinum. In addition, photocatalytic activity of N-, Pt-doped and N-Pt-codoped materials were further investigated under visible light irradiations with λ>430nm and λ>490nm. This study therefore demonstrated a promising strategy for design of highly efficient photocatalysts for remediation of aqueous pollutants.